1. Field of the Invention
The present invention relates in general to a switching device. More specifically, it relates to a hot-swap device allowing on-line switching of the power source of a system without causing the system to crash.
2. Description of the Related Art
A relay is a popular switching devices applied to perform switching operation. However, the relay can not perform a switching operation without introducing a time delay because of its mechanism and structure. Therefore, electronic systems using relays for switching operation may crash due to the switching delay of the relays. For example, using a relay to switch one battery set to the other battery set supplying power to a notebook computer could make the notebook computer crash.
FIG. 1 schematically shows a conventional swapping circuit for switching two battery sets installed in a notebook computer. Referring to FIG. 1, one of the two batter sets 12 and 14 is selected by a relay 10 to supply power to a notebook computer 16. For example, the battery set 12 first supplies power to the notebook computer 16. When the battery set 12 is going to run out of its power and users want to replace the battery set 12 with a new one without shutting down the notebook computer 16, the power supplied to the notebook computer 16 is swapped form the battery set 12 to the battery set 14 via the control of the relay 10. Then users can take out the battery set 12 and install a new one. When the relay 10 performs the switching operation, the metal rod or slice 10P (in FIG. 1) moves from the terminal A to the terminal B so that the notebook computer 16 obtains power from the battery set 14 instead of the battery set 12. However, the metal rod or slice 10P does not move from terminal A to terminal B instantly; some switching delay is inevitable. Therefore, the notebook computer 16 does not obtain steady power during the period when the metal rod or slice 10P moves from terminal A to terminal B. Accordingly, the notebook computer may crash. Moreover, the more aged the relay 10, the longer the switching delay is, and the possibility of the notebook computer crashing is increased.